The present invention relates to a method of mobile communication for transmitting and receiving data between a base station and a plurality of mobile terminals after having determined schedules for transmitting data, and to an apparatus therefor. Particularly, the invention relates to a method of mobile communication wherein, in transmitting a plurality of data packets from mobile terminals to the base station, the base station is informed that the data packets to be transmitted are present in the mobile terminals, and wherein the schedules for transmitting and receiving the data packets are determined and then the data packets are transmitted and received.
In the prior art, a reservation-type mobile communication system has been proposed to transmit and receive data by radio communication between a base station and a plurality of mobile terminals after having reserved data channels for transmission and reception.
The present inventors have developed a system for overcoming the problems associated with the conventional system as discussed below. The above-mentioned conventional mobile communication system of the reservation type has been provided with a plurality of channels such as a preservation channel for transmitting and receiving a reservation packet, a response channel for transmitting and receiving a response packet for the reservation packet, and data channels for transmitting and receiving data, and wherein mobile terminals which wish to transmit the data use the reservation channel to transmit the reservation packet to the base station in order to let the base station know the presence of data that are to be transmitted.
The base station that has received the reservation packet from the mobile terminal assigns a data channel and a time slot which is a transmission timing that will be used by the mobile terminal, and transmits the assigned data channel and the time slot to the mobile terminal by using the response channel.
The mobile terminal that has received a response from the base station transmits data to the base station by using the assigned data channel and the time slot. The mobile terminal of the conventional transmission system of the reservation type transmits the data by using the data channel and the time slot assigned by the base station, and avoids the collision of data on the data channel even when the data are transmitted from a plurality of mobile terminals.
In the above-mentioned conventional mobile communication system of the reservation type, however, a plurality of reservation packets collide in the base station when the reservation packets are transmitted from a plurality of mobile terminals to the base station, and the contents of the reservation packets cannot be correctly read out in the base station. Therefore, the mobile terminals must transmit reservation packets again. In order to transmit the reservation package again as described above, waiting times are set in a random fashion so that the reservation packages will not collide again. When the reservation packets collide, the transmission efficiency of data greatly decreases.
Furthermore, in the above-mentioned conventional mobile communication system of the reservation type, data for making a reservation are transmitted and received in addition to the data that are to be transmitted. Therefore, a ratio of the data that are desired to be transmitted decreases in the whole data that are transmitted and received between the base station and the mobile terminals. When the consecutive data are to be transmitted being divided into a plurality of data packages in the above-mentioned conventional mobile communication system of the reservation type, in particular, a reservation packet is transmitted for the transmission of each data packet, and the packets occupy a large ratio in the whole data transmitted and received between the base station and the mobile terminal.
A mobile communication system of the reservation type applying a code division multiple access (CDMA) has been disclosed in an article to R. Esmailzadeh, N. Doi, H. Masui, Y. Ohgoshi and T. Yano, entitled xe2x80x9cSpread Spectrum Slot Reservation Multiple Accessxe2x80x9d, IEEE VTC, April 1996, Vol. 3, pp. 1715-1719. The outline of this system involves forming a plurality of reservation channels, response channels and data channels by using pseudo noise (PN) as a plurality of different dispersion codes, requesting the transmission of data through the plurality of reservation channels, and transmitting and receiving data by using a data channel designated by the response channel. According to the conventional mobile communication system of the reservation type using the above-mentioned CDMA, the contents of the reservation packets can be correctly read out by the base station even when a plurality of mobile terminals are transmitting reservation packets to the base station. A plurality of reservation packets received by the base station are partially overlap each other on the time axis, provided the timings deviate by more than a chip which is a minimum unit for constituting a PN signal among the reservation packets.
However, in the conventional mobile communication system of the reservation type using the above-mentioned CDMA, when the deviation of timing is not larger than a chip among the reservation packets that are partly overlapping one another, the contents of the reservation packets are not correctly read by the base station. Therefore, the mobile terminals must transmit the reservation packets again. Also, the data for making a reservation are transmitted and received in addition to the data that are to be transmitted. Therefore, the ratio of the data that are desired to be transmitted becomes low with respect to the entire amount of data transmitted and received between the base station and the mobile terminals.
The present inventors have studied the above-mentioned prior art and have found the following problems. First, in the above-mentioned conventional mobile communication system of the reservation type, it is not possible to read the contents of the reservation packets when the reservation packets simultaneously arrive at the base station from a plurality of mobile terminals. When the plurality of reservation packets collide, it becomes necessary to transmit the reservation packets again.
Second, reservation packets are transmitted for determining schedules for transmitting data. For this purpose, therefore, an output is necessary for transmitting the reservation packets in addition to an output for transmitting the data, and the communication capacity of data decreases by an amount corresponding to the electric power of transmitting the reservation packets.
An object of the present invention is to provide technology capable of efficiently transmitting and receiving data between the base station and a plurality of mobile terminals.
Another object of the present invention is to provide technology capable of detecting the individual alert signals even when a plurality of alert signals are transmitted from a plurality of mobile terminals to the base station.
Yet another object of the present invention is to provide technology capable of maintaining, at a low level, the value of the alert signals transmitted from the mobile terminals.
The following are representative examples of methods and apparatuses which realize the above-mentioned and other objects of the present invention.
(1) A method of mobile communication includes determining schedules for transmitting and receiving data, and transmitting and receiving data between a base station and a plurality of mobile terminals according to the schedules. Particular orthogonal codes are transmitted from mobile stations to the base station as alert signals indicating the presence of data to be transmitted. The base station checks whether particular orthogonal codes are contained in the alert signals transmitted from the mobile terminals to the base station. When the particular orthogonal codes are detected in the alert signals transmitted from the mobile stations to the base station, data representing the detected orthogonal codes and the schedules for transmitting the data from the mobile terminals to the base station are transmitted from the base station to the mobile terminals as an alert response in response to the alert signals. When the data representing the orthogonal codes used for the alert signals transmitted from the mobile terminals to the base station are contained in the alert response transmitted from the base station to the mobile terminals, the data transmission schedules in the alert response are read out at the mobile terminals and the data are transmitted from the mobile terminals to the base station according the schedules that are read out.
When the data are to be transmitted and received between the base station and the mobile terminals according to the above-mentioned mobile communication method, mobile terminals which intend to transmit data select and generate particular orthogonal codes out of a plurality of orthogonal codes, and transmit these generated orthogonal codes to the base station as alert signals indicating the presence of data that are to be transmitted. Here, the orthogonal codes transmitted as alert signals from the mobile terminals to the base station are such codes that the inner products of the same codes assume particular values but the inner products of different codes assume a value of zero.
The base station that has received the alert signals generates orthogonal codes and checks whether these generated orthogonal codes are contained in the alert signals transmitted from the mobile terminals to the base station. When the orthogonal codes generated by the base station are detected in the alert signals transmitted from the mobile terminals to the base station, the base station that has received the alert signals determines schedules for transmitting the data from the mobile terminals to the base station. Then the base station transmits, to the mobile terminals, the data representing the detected orthogonal codes and the determined schedules for transmitting data from the mobile terminals to the base station as an alert response to the alert signals.
Upon receiving the alert response, the mobile terminals compare the orthogonal codes transmitted from the mobile terminals to the base station with orthogonal codes represented by the data stored in the alert response, and check if the data representing the orthogonal codes used in the alert signals transmitted from the mobile terminals to the base station are contained in the alert response transmitted from the base station to the mobile terminals. When the data representing the orthogonal codes used by a mobile terminal as its alert signal are contained in the alert response from the base station, the data transmission schedules in the alert response are read out by the mobile terminal, and the data are transmitted from the mobile terminal to the base station according to the schedules that are read out.
According to the mobile communication method as described above, the data are transmitted and received after the schedules are determined by alert signals of orthogonal codes. Therefore, an efficient communication of data can be accomplished between the base station and the plurality of mobile terminals.
(2) In the mobile communication method described in (1) above, the alert signals transmitted from the mobile terminals to the base station are multiplied by each of a plurality of orthogonal codes generated in the base station in order to check whether particular orthogonal codes are contained in the alert signals. The base station generates a plurality of orthogonal codes upon receiving alert signals from the mobile terminals, multiplies the alert signals transmitted from the mobile terminals to the base station by each of a plurality of orthogonal codes generated by the base station, and detects orthogonal codes in the alert signals that are received based upon the results of multiplication.
When a plurality of mobile terminals simultaneously transmit alert signals to the base station, a plurality of orthogonal codes are contained in the alert signals received by the base station. Here, however, the inner products of the same orthogonal codes assume particular values and the inner products of different orthogonal codes assume a value of zero. Therefore, the alert signals containing a plurality of orthogonal codes are multiplied by each of a plurality of orthogonal codes generated by the base station, and the results of multiplication are checked for each of the orthogonal codes. Even when the plurality of orthogonal codes are contained in the alert signals, therefore, it is possible to check if particular orthogonal codes are contained.
According to the mobile communication method as described above, the results of multiplication of the same orthogonal codes assume particular values and the results of multiplication of different orthogonal codes assume a value of zero. This makes it possible to detect the individual alert signals even when the plurality of alert signals are transmitted from a plurality of mobile terminals to the base station.
(3) In the mobile communication method described in (2) above, the results of multiplication of the alert signals transmitted from the mobile terminals to the base station and the orthogonal codes generated in the base station, are accumulated for each of a plurality of bit periods constituting the orthogonal codes in order to check whether particular orthogonal codes are contained in the alert signals. Upon receiving alert signals from the mobile terminals, the base station multiplies the alert signals transmitted from the mobile terminals to the base station by orthogonal codes generated by the base station, and accumulates the results of the multiplication for each of a plurality of bit periods constituting the orthogonal codes. When the inner products of the orthogonal codes in the alert signals that are received and the orthogonal codes generated by the base station are accumulated for each of a plurality of bit periods, the noise component in each bit period is canceled and the S/N ratio of the alert signals is improved. Therefore, it becomes possible to maintain the output value of the alert signals transmitted from the mobile terminals at a low level. This saves the output of the alert channel for transmitting the alert signals and increases the number of data channels.
According to the mobile communication method as described above, reception of the alert signals is detected by accumulating the orthogonal codes for a plurality of bit periods, making it possible to maintain the output value of the alert signals transmitted from the mobile terminals at a low level.
(4) An apparatus used for mobile communication according to a method involving determining schedules for transmitting and receiving data, and transmitting and receiving data between a base station and a plurality of mobile terminals according to the schedules, includes an alert signal transmission means for transmitting particular orthogonal codes from mobile terminals to the base station as alert signals indicating the presence of data to be transmitted. The apparatus also includes an alert signal reception means for checking in the base station whether particular orthogonal codes are contained in the alert signals transmitted from the mobile terminals to the base station. An alert response transmission means is provided which, when the particular orthogonal codes are detected in the alert signals transmitted from the mobile terminals to the base station, transmits, from the base station to the mobile terminals, data representing the detected orthogonal codes and the schedules for transmitting the data from the mobile terminals to the base station as an alert response to the alert signals. Finally, an alert response reception means is provided which, when the data representing the orthogonal codes used for the alert signals transmitted from the mobile terminals to the base station are contained in the alert response transmitted from the base station to the mobile terminals, reads out at the mobile terminals the data transmission schedules in the alert response.
When the data are to be transmitted and received between the base station and the mobile terminals according to the above-mentioned mobile communication apparatus, mobile terminals which intend to transmit data select and generate particular orthogonal codes out of a plurality of orthogonal codes, and transmit these generated orthogonal codes to the base station as alert signals indicating the presence of data for transmitting the above generated orthogonal codes. In the base station which has received the alert signals, the alert signal reception means generates orthogonal codes and checks if the above generated orthogonal codes are contained in the alert signals that are transmitted from the mobile terminals to the base station. When the orthogonal codes generated by the base station are detected in the alert signals transmitted from the mobile terminals to the base station, the alert response transmission means in the base station that has received the alert signals determines schedules for transmitting data from the mobile terminals to the base station, and transmits, from the base station to the mobile terminals, the data representing the detected orthogonal codes and the determined schedules for transmitting data from the mobile terminals to the base station as an alert response to the alert signals.
In the mobile terminals that have received the alert response, the alert response reception means compares the orthogonal codes transmitted from the mobile terminals to the base station with orthogonal codes represented by the data stored in the alert response, and checks if the data representing the orthogonal codes used in the alert signals transmitted from the mobile terminals to the base station are contained in the alert response transmitted from the base station to the mobile terminals. When the data representing the orthogonal codes used by the mobile terminals as alert signals are contained in the alert response from the base station, the data transmission schedules in the alert response are read out by the mobile terminals, and the data are transmitted from the mobile terminals to the base station according to the schedules that are read out.
According to the mobile communication apparatus as described above, the data are transmitted and received after the schedules are determined by alert signals which use orthogonal codes. Therefore, an efficient communication of data can be accomplished between the base station and the mobile terminals.
(5) In an apparatus for mobile communication described in (4) above, the alert signal reception means is provided with a multiplication means for multiplying the alert signals transmitted from the mobile terminals to the base station by each of a plurality of orthogonal codes generated in the base station. When the base station in the above-mentioned mobile communication apparatus receives alert signals from the mobile terminals, the alert signal reception means generates a plurality of orthogonal codes, and the multiplication means multiplies the alert signals transmitted from the mobile terminals to the base station by each of a plurality of orthogonal codes generated by the base station, in order to detect orthogonal codes in the alert signals that are received based upon the results of multiplication. When a plurality of mobile terminals simultaneously transmit alert signals to the base station, a plurality of orthogonal codes are contained in the alert signals received by the base station. Here, however, the inner products of the same orthogonal codes assumes particular values and the inner products of different orthogonal codes assume a value of zero. Therefore, the alert signals containing a plurality of orthogonal codes are multiplied by each of a plurality of orthogonal codes generated by the base station, and the results of multiplication are checked for each of the orthogonal codes. Even when the plurality of orthogonal codes are contained in the alert signals, therefore, it is possible to check if particular orthogonal codes are contained.
According to the mobile communication apparatus as described above, the results of multiplication of the same orthogonal codes assume particular values and the results of multiplication of different orthogonal codes assume a value of zero. This makes it possible to detect the individual alert signals even when the alert signals are transmitted from the mobile terminals to the base station.
(6) In the mobile communication apparatus described in (5) above, the alert signal reception means is provided with an accumulation means for accumulating the results of multiplication of the alert signals transmitted from the mobile terminals to the base station and the orthogonal codes generated in the base station for each of a plurality of bit periods constituting the orthogonal codes. When the base station receives alert signals from the mobile terminals, the alert signal reception means multiplies the alert signals transmitted from the mobile terminals to the base station by orthogonal codes generated by the base station, and the accumulation means accumulates the results of multiplication for each of a plurality of bit periods constituting the orthogonal codes. When the inner products of the orthogonal codes in the alert signals that are received and the orthogonal codes generated by the base station are accumulated for each of a plurality of bit periods constituting the orthogonal codes, the noise component in each bit period is canceled and the S/N ratio of the alert signals is improved. Therefore, it becomes possible to maintain the output value of the alert signals transmitted from the mobile terminals in the mobile communication apparatus at a low level. This saves the output of the alert channel for transmitting the alert signals and increases the number of data channels.
According to the mobile communication apparatus as described above, reception of the alert signals is detected by accumulating the orthogonal codes for a plurality of bit periods, making it possible to maintain the output value of the alert signals transmitted from the mobile terminals at a low level.
These and other objects, features and advantages of the present invention will become more apparent in view of the following detailed description of the preferred embodiments in conjunction with the accompanying drawings.